Manufacturing of decorative surfaces by inkjet

ABSTRACT

A method of manufacturing a decorative surface includes the steps of a) impregnating a paper substrate with a thermosetting resin; b) jetting a colour pattern with one or more aqueous inkjet inks including a polymer latex binder on the thermosetting resin impregnated paper; c) drying the one or more aqueous inkjet inks; and d) heat pressing the thermosetting paper carrying the colour pattern into a decorative surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2014/071733, filed Oct. 10, 2014. This application claims thebenefit of European Application No. 13189667.2, filed Oct. 22, 2013,which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the manufacturing of decorativesurfaces using inkjet technology.

2. Description of the Related Art

Gravure, offset and flexography are being increasingly replaced fordifferent applications by industrial inkjet printing systems, which havenow proven their flexibility in use, such as variable data printingmaking short production runs and personalized products possible, andtheir enhanced reliability, allowing incorporation into productionlines.

Inkjet technology has also caught the attention of manufacturers ofdecorative surfaces, such as laminate floor. In the current productionprocess for manufacturing decorative panels as shown by FIG. 1, a papermanufacturer (11) supplies a paper roll (12) to a decor printer (13) whouses gravure printing (14) in order to deliver a decor paper roll (16)to a warehouse (17) of a floor laminate manufacturer (20). Some decorprinters (13) are now investigating inkjet printing (15) instead ofgravure printing. Rotogravure printing on the porous décor papergenerally uses ink having a viscosity at 25° C. of 1 to 2 Pa·s. Theviscosity of inkjet inks is much lower, often about 1 to 15 mPa·s at 25°C., which makes it necessary to use a more expensive paper having aspecial ink-receiving layer in order to obtain a good image quality. Thefloor laminate manufacturer (20) stores the decor paper rolls (16)having different decorative patterns in his warehouse (17). Depending onthe market demand, the floor laminate manufacturer (20) then selects thedecor rolls (16) with the desired decorative pattern in his warehouse(17). The selected decor rolls (16) are then impregnated (18) and cut tosize (19) for manufacturing ready-to-use floor laminate (21). Thewarehouse (17) is necessary as a buffer for sudden large market demandsof a specific floor laminate because there is a large time delay betweenordering and delivering of new decorative paper rolls (16).

An approach to reduce the size of the warehouse and time delays istreated by EP 2431190 A (THEODOR HYMMEN), which discloses in FIG. 1 amethod for producing a digitally printed sheet, web or plate-shapedworkpiece (20) with wear-resistant surface including the steps of: A)providing a digital data set to a digital printing device (1); B)providing a printable workpiece (20) to the printing apparatus (1); C)digital printing at least an acrylate printing ink (22) on the printableworkpiece (20) using the printing apparatus (1) and thereafter supplyinga resin mixture (5, 21) to the digitally printed workpiece; and D)curing the resin mixture (5, 21) by means of a heated press (7). Thetime delay can be avoided by the floor laminate manufacturerincorporating the manufacturing of decorative paper rolls into its ownproduction process. EP 2431190 A (THEODOR HYMMEN) discloses in FIG. 2the use of a paper substrate having a special ink receiving layer (23),which in combination with a more expensive acrylate ink only increasesthe cost of the final product. Furthermore, paragraph [0003] disclosesthat the use of acrylate ink leads to adhesion problems between thereactive melamine resin mixture and the acrylate ink, requiring specificmeasures like crosslinking agents that react only above 50° C. or 70°C., making the manufacturing process less robust.

EP2574476 A (TRESPA) discloses a method for producing a decorative filmcomprising a resin-impregnated substrate paper provided with one or moretop layers, characterised in that the method comprises the followingsteps: i) providing a resin-impregnated substrate paper; ii) printingthe substrate paper obtained in step i) with an ink composition, usinginkjet technology; iii) subjecting the substrate paper printed with anink composition as obtained after step ii) to a treatment of the dryingand/or curing type; iv) applying at least one transparent top layer tothe paper obtained after step iii); and v) curing the paper obtainedafter step iv) to obtain the decorative film. EP 1700689 A (DAI NIPPONPRINTING CO) discloses a decorative material comprising a surface layerand a base material layer laminated and integrated on a rear surfacethereof, characterized in that the surface layer comprises at least asurface resin layer made of a cured material of an ionizing radiationcuring resin, a blocking layer for blocking an ooze out of an uncuredmaterial of a thermosetting resin, and an impregnated paper layer formedby a paper impregnated with the thermosetting resin and cured, laminatedfrom a surface side; and at least an uppermost surface of the basematerial layer comprises the impregnated paper layer formed by the paperimpregnated with the thermosetting resin and cured. WO 2013/050910 A(UNILIN) discloses a Floor panel comprising a core (13), a print (16)and a wear resistant layer (17), wherein the core (13) is assembled atleast from a plurality of paper sheets, or other carrier sheets (14),impregnated with a thermosetting resin (15).

Although EP2574476 A, EP 1700689 A and WO 2013/050910 A mention the useof inkjet printing in manufacturing decorative panels, they are allsilent on the use of aqueous polymer latex based inkjet inks.

Hence, there is still a need for improved manufacturing methods ofdecorative surfaces using inkjet technology and melamine resin as a wearcoating.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention relate to a method for manufacturing decorativesurfaces as defined below.

A much simpler solution has been found by rethinking the entiremanufacturing process. One important aspect is the change of order ofresin impregnation and printing. The prior art systems, as shown in FIG.1, all first print a decorative colour pattern on paper by gravure orinkjet and then impregnate the printed paper by thermosetting resin. Inour invention, the paper is first impregnated and then printed byinkjet, using aqueous inks that contain a polymer latex binder. Thiseliminates the need for a special ink-receiving layer on the papersubstrate, in order to obtain good image quality. Simultaneouslyproblems of incomplete and inhomogeneous resin impregnation due to thepresence of such an ink-receiving layer on the paper surface are alsoavoided.

It was also observed that a too high ink lay down caused adhesionproblems and blister formation when the different layers areheat-pressed together to form a decorative panel. A thermosetting resin,like a melamine formaldehyde resin (MF), polycondensates when exposed toheat in a pressing operation. The polycondensation reaction of MF resincreates water as a by-product, which must leave the hardening resinlayer. The ink layer acts as a barrier layer for this water vapour,resulting in the observed adhesion problems and blister formation.

The major advantageous effect of invention is the much simplermanufacturing process of decorative panels, which is immediately visibleby comparing FIG. 1 and FIG. 2 showing that our invention requires nolonger an intermediate décor printer company (13) or a warehouse (17).Printing in-house at the floor laminate manufacturer (20) allows formaximum flexibility. Changes in design of a decorative colour patterncan be rapidly introduced in production, thereby also minimizingdependency on supply by the décor printer company (13). There are alsono longer minimum purchase quantities to be negotiated with the décorprinter company (13). In-house printing allows for fast adaptability tomarket trends and an increase of product variety without substantialfinancial penalties.

The replacement of gravure by inkjet also has many advantages. There isno longer a storage of gravure rolls necessary. Furthermore, inkjetallows easy colour reproduction compared to the time consuming colourmatching issues in gravure which usually may take up to 5 hours oftuning. This immediately also illustrates that short print runs usinginkjet is much more cost-efficient than gravure.

Resin impregnation can cause major paper loss. Financial loss isminimized if the paper is first impregnated and then inkjet printed,because less digital print has to be thrown away. Another advantage offirst impregnating and then inkjet printing is dimensional stability,allowing for a wood grain to be embossed in perfect alignment of theinkjet printed wood colour pattern.

Further advantages and preferred embodiments of the present inventionwill become apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the prior art production process for manufacturingdecorative panels, wherein a paper manufacturer (11) supplies a paperroll (12) to a decor printer (13) using gravure printing (14) or inkjetprinting (15) in order to deliver a decor paper roll (16) to a warehouse(17) of a floor laminate manufacturer (20). Depending on the marketdemand, the floor laminate manufacturer (20) selects one of thedifferent decor rolls in his warehouse (17) to impregnate (18) and tocut to a size (19) for being heat pressed and finished into ready-to-usefloor laminate (21).

FIG. 2 shows a production process for manufacturing decorative panels,wherein a paper manufacturer (11) supplies a paper roll (12) directly toa floor laminate manufacturer (20) who impregnates (18) the paper roll(12), cuts to a size (19) for being inkjet printed (15) and then heatpressed and finished into ready-to-use floor laminate (21). The order ofcutting to size (19) and inkjet printing (15) may also be reversed, i.e.printing on a impregnated paper roll before cutting to sheets.

FIG. 3 shows a cross-section of a decorative panel (30) including a corelayer (31) with a groove (32) and tongue (33) which is laminated on thetop side by a decorative layer (34) and a protective layer (35) and onthe back side by a balancing layer (36).

FIG. 4. shows a cross section of a decorative panel (30) having amechanical join by a tongue (33) and a groove (32) requiring no glue.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Definitions

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. methyl, ethyl, for three carbon atoms:n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl andtertiary-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl,2,2-dimethylpropyl and 2-methyl-butyl, etc.

Unless otherwise specified a substituted or unsubstituted alkyl group ispreferably a C₁ to C₆-alkyl group.

Unless otherwise specified a substituted or unsubstituted alkenyl groupis preferably a C₁ to C₆-alkenyl group.

Unless otherwise specified a substituted or unsubstituted alkynyl groupis preferably a C₁ to C₆-alkynyl group.

Unless otherwise specified a substituted or unsubstituted aralkyl groupis preferably phenyl group or naphthyl group including one, two, threeor more C₁ to C₆-alkyl groups.

Unless otherwise specified a substituted or unsubstituted alkaryl groupis preferably a C₁ to C₆-alkyl group including a phenyl group ornaphthyl group.

Unless otherwise specified a substituted or unsubstituted aryl group ispreferably a phenyl group or naphthyl group.

Unless otherwise specified a substituted or unsubstituted heteroarylgroup is preferably a five- or six-membered ring substituted by one, twoor three oxygen atoms, nitrogen atoms, sulphur atoms, selenium atoms orcombinations thereof.

The term “substituted”, in e.g. substituted alkyl group means that thealkyl group may be substituted by other atoms than the atoms normallypresent in such a group, i.e. carbon and hydrogen. For example, asubstituted alkyl group may include a halogen atom or a thiol group. Anunsubstituted alkyl group contains only carbon and hydrogen atoms

Unless otherwise specified a substituted alkyl group, a substitutedalkenyl group, a substituted alkynyl group, a substituted aralkyl group,a substituted alkaryl group, a substituted aryl and a substitutedheteroaryl group are preferably substituted by one or more substituentsselected from the group consisting of methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl and tertiary-butyl, ester, amide, ether,thioether, ketone, aldehyde, sulfoxide, sulfone, sulfonate ester,sulphonamide, —Cl, —Br, —I, —OH, —SH, —CN and —NO₂.

Methods for Manufacturing Decorative Surfaces

The method for manufacturing decorative surfaces according to apreferred embodiment of the present invention includes the steps of: a)impregnating a paper substrate with a thermosetting resin; b) inkjetprinting a colour pattern with one or more aqueous inkjet inks includinga polymer latex binder on the thermosetting resin impregnated paper; andc) heat pressing the thermosetting paper carrying the colour patterninto a decorative surface. The presence of a polymer latex in theaqueous inkjet ink results in a good image quality without causingadhesion problems or blisters when heat pressed into floor laminate

The paper of the decorative surface is first impregnated with athermosetting resin before being inkjet printed upon. In one preferredembodiment, the thermosetting resin impregnated paper is first inkjetprinted and then cut into a sheet.

In a preferred embodiment, as also shown in FIG. 2, the thermosettingresin impregnated paper is first cut into a sheet and then inkjetprinted. In the latter, financial losses due to cutting errors isminimized.

The amount of ink lay down for printing the colour pattern is preferablyless than 6 g/m² ink as dry weight. A higher amount can lead todelamination, i.e. adhesion problems, because the ink layer acts as abarrier layer for water vapour formed by the crosslinking of thethermosetting resin.

In a preferred embodiment of the manufacturing method, the thermosettingresin impregnated paper includes a coloured paper substrate, morepreferably a bulk coloured paper substrate. The use of a coloured papersubstrate reduces the amount of inkjet ink required to form the colourpattern.

In a preferred embodiment of the manufacturing method, the colouredpaper substrate is prepared by impregnating the paper substrate with acoloured thermosetting resin.

In another preferred embodiment of the manufacturing method, thecoloured paper substrate is prepared by coating a coloured layer on thepaper substrate, preferably on the resin impregnated paper substrate.

In a preferred embodiment, the one or more aqueous inkjet inks are oneor more pigmented aqueous inkjet inks.

In a preferred embodiment of the manufacturing method, the one or moreaqueous inkjet inks include an aqueous inkjet ink containing a colourpigment selected from the group consisting of C.I Pigment Yellow 151,C.I. Pigment Yellow 74, and mixed crystals thereof

In a preferred embodiment of the manufacturing method, the one or moreaqueous inkjet inks include an aqueous inkjet ink containing a colourpigment selected from the group consisting of C.I Pigment Red 254, C.I.Pigment Red 122, and mixed crystals thereof.

In a preferred embodiment of the manufacturing method, the one or moreaqueous inkjet inks form an aqueous inkjet ink set including:

a) a cyan aqueous inkjet ink containing a copper phthalocyanine pigment;

b) a red aqueous inkjet ink containing a colour pigment selected fromthe group consisting of C.I Pigment Red 254, C.I. Pigment Red 122, andmixed crystals thereof;

c) a yellow aqueous inkjet ink containing a colour pigment selected fromthe group consisting of C.I Pigment Yellow 151, C.I. Pigment Yellow 74,and mixed crystals thereof; and

d) a black aqueous inkjet ink containing carbon black pigment. The useof such an aqueous CRYK inkjet ink set allows reducing the amount ofinkjet ink required to reproduce a wooden décor for a floor laminate.

In a preferred embodiment of the manufacturing method, the thermosettingresin is a melamine based resin.

In a preferred embodiment of the manufacturing method, the one or moreaqueous inkjet inks are inkjet printed at a jetting temperature of notmore than 35° C.

For having a good ejecting ability and fast inkjet printing, theviscosity of the one or more aqueous inkjet inks at a temperature of 32°C. is preferably smaller than 30 mPa·s, more preferably smaller than 15mPa·s, and most preferably between 1 and 10 mPa·s all at a shear rate of1,000 s⁻¹. A preferred jetting temperature is between 10 and 70° C.,more preferably between 20 and 40° C., and most preferably between 25and 35° C.

In a preferred embodiment of the manufacturing method, the thermosettingresin impregnated paper carrying the colour pattern is heat pressedbetween a protective layer containing a thermosetting resin and a corelayer, with the colour pattern facing the protective layer. In thelatter, the thermosetting resin impregnated paper includes a whiteningagent for masking surface defects of the core layer.

In another preferred embodiment of the manufacturing method, thethermosetting resin impregnated paper carrying the colour pattern isheat pressed as a protective layer into a decorative surface, with thecolour pattern facing towards a core layer present in the decorativesurface. In the latter, the protective layer (or overlay) includes athermosetting resin impregnated paper containing no or substantially nowhitening agent because the overlay becomes transparent after heatpressing so that the colour pattern van be viewed. The colour patternmust face the core layer because otherwise the colour pattern wouldrapidly deteriorate through wear.

In a preferred embodiment of the manufacturing method, the protectivelayer includes hard particles in an amount between 1 g/m² and 100 g/m².

In a preferred embodiment of the manufacturing method, the thermosettingresin is a melamine based resin. A melamine based resin is preferred notonly because of its excellent physical properties against wear, but alsobecause of the clear transparency after heat pressing showing nodiscolouration.

In a preferred embodiment of the manufacturing method, the polymer latexbinder is a polyurethane based latex binder because of its highcompatibility with a thermosetting resin, especially its highcompatibility with a melamine based resin.

In a preferred embodiment of the manufacturing method, the inkjetprinting is performed by a single pass printing inkjet printing process.This allows for a high productivity (m² decorative surface per hour).

In a preferred embodiment, the method of manufacturing a decorativesurface comprises the step of hot pressing at least the core layer andthe decorative layer which includes a colour pattern and a thermosettingresin provided paper. Preferably the method of the invention forms partof a DPL process as above described, wherein the decorative layer istaken up in a stack to be pressed with the core layer and a balancinglayer, and preferably also a protective layer. It is of course notexcluded that the method of the invention would form part of a CPL(Compact Laminate) or an HPL (High Pressure Laminate) process in whichthe decorative layer is hot pressed at least with a plurality of resinimpregnated core paper layers, e.g. of so called Kraft paper, forming asubstrate underneath the decorative layer, and wherein the obtainedpressed and cured laminate layer, or laminate board is, in the case ofan HPL, glued to a further substrate, such as to a particle board or anMDF or HDF board.

In a preferred embodiment, a protective layer containing a thermosettingresin is applied onto the inkjet printed colour pattern, wherein thethermosetting resin may be a colored thermosetting resin to reduce theamount of inkjet ink to be printed.

In a particularly preferred embodiment of the manufacturing method, atleast the protective layer includes a relief 37 corresponding to thecolour pattern. The relief in at least the protective layer ispreferably provided by means of a short cycle embossing press. Theembossing preferably takes place at the same time that the core layer,the decorative layer and the protective layer, and preferably also oneor more balancing layers, are pressed together.

Preferably the relief comprises portions that have been embossed over adepth of more than 0.5 mm, or even more than 1 mm, with respect to theglobal upper surface of the decorative panel. The embossments may extendinto the decorative layer.

The balancing layer of a decorative panel is preferably planar. However,a relief might be applied in the balancing layer(s) for improving gluingdown of the panels and/or for improved slip resistance and/or forimproved, i.e. diminished, sound generation or propagation.

It should be clear that the use of more than one press treatment is alsoadvantageous for the present method of manufacturing decorativesurfaces. Such technique could be used for the manufacturing of anypanel that comprises on the one hand a wear resistant protective layeron the basis of a thermosetting synthetic material, possibly a carriersheet such as paper, and hard particles, and, on the other hand, one ormore layers underlying the wear resistant protective layer on the basisof thermosetting synthetic material. The underlying layers comprise adecorative layer, being an inkjet printed paper provided withthermosetting resin, wherein aqueous inks containing a polymer latexbinder have been used during the inkjet printing. As a core layer, suchpanel might essentially comprise a board material with a density of morethan 500 kg/m³, such as an MDF or HDF board material. The manufacturingpanels with a plurality of press treatments is preferably put inpractice with the so-called DPL panels (Direct Pressure Laminate). Inthe latter case, during a first press treatment, at least the decorativelayer provided with thermosetting resin, is cured and attached to thecore material, preferably an MDF or HDF board material, whereby a wholeis obtained of at least the decorative layer and the board material, andpossibly a balancing layer at the side of the board opposite the decorlayer. During a second press treatment, the wear resistant layer iscured and attached to the obtained whole.

In another preferred embodiment, the method for manufacturing adecorative surface uses inkjet printing in combination with themethodology disclosed by US 2011008624 (FLOORING IND), wherein theprotective layer includes a substance that hardens under the influenceof ultraviolet light or electron beams.

In a very preferred embodiment, the method of manufacturing ofdecorative surface includes the following steps: 1) impregnating a paperwith a thermosetting resin; 2) inkjet printing, as described above,namely by means of polymer latex binder containing inks, a colourpattern on the thermosetting resin impregnated paper to produce adecorative layer; and 3) applying the decorative layer and a protectivelayer including a thermosetting resin impregnated paper on a mostlywood-based core layer by means of a short cycle embossing press andoptionally at the same time creating relief in at least the protectivelayer. The thermosetting resin used in step 1) and/or 3) is preferably aresin or a combination of resins selected from the group consisting ofmelamine resin, urea resin, acrylate dispersion, acrylate copolymerdispersion and polyester resins, but is preferably a melamine resin. Themostly wood-based core used in step 3) is preferably MDF or HDF.

In an even more preferred embodiment, the decorative layer and theprotective layer are applied on a mostly wood-based core layer by meansof a short cycle embossing press and at the same time a relief iscreated in at least the protective layer.

The decorative panel obtained by the above preferred manufacturingmethods preferably includes at least: 1) a transparent, preferablymelamine based, protective layer; 2) an inkjet printed colour pattern;3) a core, preferably an MDF or HDF core; and optionally 4) a relief atan upper surface, wherein the inks of the inkjet printed colour patterninclude a polymer latex binder. In a preferred embodiment, thedecorative panel includes the relief at the upper surface. In apreferred embodiment, the decorative panel has an AC3 classification,more preferably an AC4 classification in accordance with EN 13329.

Aqueous Inkjet Ink Sets

A preferred aqueous inkjet ink set for manufacturing decorative surfacesconsists of a) a cyan aqueous inkjet ink containing a copperphthalocyanine pigment; b) a red aqueous inkjet ink containing a colourpigment selected from the group consisting of C.I Pigment Red 254, C.I.Pigment Red 122, and mixed crystals thereof; c) a yellow aqueous inkjetink containing a colour pigment selected from the group consisting ofC.I Pigment Yellow 151, C.I. Pigment Yellow 74, and mixed crystalsthereof; and d) a black aqueous inkjet ink containing carbon blackpigment, wherein the aqueous inkjet inks include a polymer latex binder,more preferably a polyurethane based latex binder.

The aqueous inkjet inks preferably have a surface tension between 18.0and 45.0 mN/m at 25° C. An aqueous inkjet ink with a surface tensionsmaller than 18.0 mN/m at 25° C. includes a high amount of surfactant,which may cause problems of foaming. A surface tension greater than 45.0mN/m at 25° C. often leads to insufficient spreading of the ink on thethermosetting resin impregnated paper.

Colorants

The colorant in the one or more aqueous inkjet inks can be a dye, but ispreferably a colour pigment. The one or more pigmented aqueous inkjetinks preferably contain a dispersant, more preferably a polymericdispersant, for dispersing the pigment. The one or more may contain adispersion synergist to improve the dispersion quality and stability ofthe ink.

In another preferred embodiment of the one or more pigmented aqueousinkjet inks, the one or more pigmented aqueous inkjet inks contain aso-called “self dispersible” colour pigment. A self-dispersible colourpigment requires no dispersant, because the pigment surface has ionicgroups which realize electrostatic stabilization of the pigmentdispersion. In case of self-dispersible colour pigments, the stericstabilization obtained by using a polymeric dispersant becomes optional.The preparation of self-dispersible colour pigments is well-known in theart and can be exemplified by EP 904327 A (CABOT).

The colour pigments may be black, white, cyan, magenta, yellow, red,orange, violet, blue, green, brown, mixtures thereof, and the like. Acolour pigment may be chosen from those disclosed by HERBST, Willy, etal. Industrial Organic Pigments, Production, Properties, Applications.3rd edition. Wiley—VCH, 2004. ISBN 3527305769.

A particularly preferred pigment for a cyan aqueous inkjet ink is acopper phthalocyanine pigment, more preferably C.I. Pigment Blue 15:3 orC.I. Pigment Blue 15:4.

Particularly preferred pigments for a red aqueous inkjet ink are C.IPigment Red 254 and C.I. Pigment Red 122, and mixed crystals thereof.

Particularly preferred pigments for yellow aqueous inkjet ink are C.IPigment Yellow 151 and C.I. Pigment Yellow 74, and mixed crystalsthereof.

For the black ink, suitable pigment materials include carbon blacks suchas Regal™ 400R, Mogul™ L, Elftex™ 320 from Cabot Co., or Carbon BlackFW18, Special Black™ 250, Special Black™ 350, Special Black™ 550,Printex™ 25, Printex™ 35, Printex™ 55, Printex™ 90, Printex™ 150T fromDEGUSSA Co., MA8 from MITSUBISHI CHEMICAL Co., and C.I. Pigment Black 7and C.I. Pigment Black 11.

Also mixed crystals may be used. Mixed crystals are also referred to assolid solutions. For example, under certain conditions differentquinacridones mix with each other to form solid solutions, which arequite different from both physical mixtures of the compounds and fromthe compounds themselves. In a solid solution, the molecules of thecomponents enter into the same crystal lattice, usually, but not always,that of one of the components. The x-ray diffraction pattern of theresulting crystalline solid is characteristic of that solid and can beclearly differentiated from the pattern of a physical mixture of thesame components in the same proportion. In such physical mixtures, thex-ray pattern of each of the components can be distinguished, and thedisappearance of many of these lines is one of the criteria of theformation of solid solutions. A commercially available example isCinquasia™ Magenta RT-355-D from Ciba Specialty Chemicals.

Also mixtures of pigments may be used. For example, the inkjet inkincludes a carbon black pigment and at least one pigment selected fromthe group consisting of a blue pigment, a cyan pigment, magenta pigmentand a red pigment. It was found that such a black inkjet ink allowedeasier and better colour management for wood colours.

The pigment particles in the pigmented inkjet ink should be sufficientlysmall to permit free flow of the ink through the inkjet printing device,especially at the ejecting nozzles. It is also desirable to use smallparticles for maximum colour strength and to slow down sedimentation.

The average particle size of the pigment in the pigmented inkjet inkshould be between 0.005 μm and 15 μm. Preferably, the average pigmentparticle size is between 0.005 and 5 μm, more preferably between 0.005and 1 μm, particularly preferably between 0.005 and 0.3 μm and mostpreferably between 0.040 and 0.150 μm.

The pigment is used in the pigmented inkjet ink in an amount of 0.1 to20 wt %, preferably 1 to 10 wt %, and most preferably 2 to 5 wt % basedon the total weight of the pigmented inkjet ink. A pigment concentrationof at least 2 wt % is preferred to reduce the amount of inkjet inkneeded to produce the colour pattern, while a pigment concentrationhigher than 5 wt % reduces the colour gamut for printing the colourpattern with print heads having a nozzle diameter of 20 to 50 μm.

Dispersants

The pigmented inkjet ink preferably contains a dispersant, morepreferably a polymeric dispersant, for dispersing the pigment.

Suitable polymeric dispersants are copolymers of two monomers but theymay contain three, four, five or even more monomers. The properties ofpolymeric dispersants depend on both the nature of the monomers andtheir distribution in the polymer. Copolymeric dispersants preferablyhave the following polymer compositions:

-   -   statistically polymerized monomers (e.g. monomers A and B        polymerized into ABBAABAB);    -   alternating polymerized monomers (e.g. monomers A and B        polymerized into ABABABAB);    -   gradient (tapered) polymerized monomers (e.g. monomers A and B        polymerized into AAABAABBABBB);    -   block copolymers (e.g. monomers A and B polymerized into        AAAAABBBBBB) wherein the block length of each of the blocks (2,        3, 4, 5 or even more) is important for the dispersion capability        of the polymeric dispersant;    -   graft copolymers (graft copolymers consist of a polymeric        backbone with polymeric side chains attached to the backbone);        and    -   mixed forms of these polymers, e.g. blocky gradient copolymers.

Suitable dispersants are DISPERBYK™ dispersants available from BYKCHEMIE, JONCRYL™ dispersants available from JOHNSON POLYMERS andSOLSPERSE™ dispersants available from ZENECA. A detailed list ofnon-polymeric as well as some polymeric dispersants is disclosed by MCCUTCHEON. Functional Materials, North American Edition. Glen Rock, N.J.:Manufacturing Confectioner Publishing Co., 1990. p. 110-129.

The polymeric dispersant has preferably a number average molecularweight Mw between 500 and 30000, more preferably between 1500 and 10000.

The polymeric dispersant has preferably a weight average molecularweight Mw smaller than 100,000, more preferably smaller than 50,000 andmost preferably smaller than 30,000.

In a particularly preferred embodiment, the polymeric dispersant used inthe one or more pigmented inkjet inks is a copolymer comprising between3 and 11 mol % of a long aliphatic chain (meth)acrylate wherein the longaliphatic chain contains at least 10 carbon atoms.

The long aliphatic chain (meth)acrylate contains preferably 10 to 18carbon atoms. The long aliphatic chain (meth)acrylate is preferablydecyl (meth)acrylate. The polymeric dispersant can be prepared with asimple controlled polymerization of a mixture of monomers and/oroligomers including between 3 and 11 mol % of a long aliphatic chain(meth)acrylate wherein the long aliphatic chain contains at least 10carbon atoms.

A commercially available polymeric dispersant being a copolymercomprising between 3 and 11 mol % of a long aliphatic chain(meth)acrylate is Edaplan™ 482, a polymeric dispersant from MUNZING.

Polymer Latex Binders

The polymer latex is not particularly limited as long as it has stabledispersibility in the ink composition. There is no limitation on themain chain skeleton of the water-insoluble polymer. Examples of thepolymer include a vinyl polymer and a condensed polymer (e.g., an epoxyresin, polyester, polyurethane, polyamide, cellulose, polyether,polyurea, polyimide, and polycarbonate). Among the above, a vinylpolymer is particularly preferable because of easily controlledsynthesis.

In a particularly preferred embodiment the polymer latex is apolyurethane latex, more preferably a self-dispersible polyurethanelatex. The polymer latex binder in the one or more aqueous inkjet inksis preferably a polyurethane based latex binder for reasons ofcompatibility with the thermosetting resin.

In a particularly preferred embodiment, the one or more aqueous inkjetinks include inter-crosslinkable latex particles. Suitable examples aredisclosed by EP 2467434 A (HP), however preferably theinter-crosslinking is obtained using (meth)acrylate groups.

Preferred hydrophobic monomers for synthesizing latexes include, withoutlimitation, styrene, p-methyl styrene, methyl methacrylate, hexylacrylate, hexyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexylmethacrylate, butyl acrylate, butyl methacrylate, ethyl acrylate, ethylmethacrylate, propyl acrylate, propyl methacrylate, octadecyl acrylate,stearyl methacrylate, vinylbenzyl chloride, isobornyl acrylate,tetrahydrofurfuryl acrylate, 2-phenoxyethyl methacrylate, ethoxylatednonyl phenol methacrylate, isobornyl methacrylate, cyclohexylmethacrylate, t-butyl methacrylate, n-octyl methacrylate, laurylmethacrylate, tridecyl methacrylate, alkoxylated tetrahydrofurfurylacrylate, isodecyl acrylate, isobornylmethacrylate, derivatives thereof,and mixtures thereof.

The polymerized monomers of the latex particulates preferably include acrosslinker that crosslinks the polymerized monomers and enhances thedurability of the composite latex particulate. Suitable cross-linkingmonomers are polyfunctional monomers and oligomers such as, withoutlimitation, ethylene glycol dimethacrylate, diethylene glycoldimethacrylate, ethylene glycol diacrylate, diethylene glycoldiacrylate, 1,6-hexanediol diacrylate, tetraethylene glycol diacrylate,tripropylene glycol diacrylate, ethoxylated bisphenol A diacrylate,pentaerythritol tri- and tetraacrylate, N,N′-methylenebisacrylamide,divinylbenzene and combinations thereof, mixtures thereof, andderivatives thereof. When present, the cross-linkers preferably comprisefrom 0.1 wt % to 15 wt % of the polymerized monomers.

The polymer latex in the invention is preferably a self-dispersingpolymer latex, and more preferably a self-dispersing polymer latexhaving a carboxyl group, from the viewpoint of ejecting stability andstability of the liquid (particularly, dispersion stability) when usinga colour pigment. The self-dispersing polymer latex means a latex of awater-insoluble polymer that does not contain a free emulsifier and thatcan get into a dispersed state in an aqueous medium even in the absenceof other surfactants due to a functional group (particularly, an acidicgroup or a salt thereof) that the polymer itself has.

In preparing a self-dispersing polymer latex, preferably a monomer isused selected from the group consisting of an unsaturated carboxylicacid monomer, an unsaturated sulfonic acid monomer, and an unsaturatedphosphoric acid monomer.

Specific examples of the unsaturated carboxylic acid monomer includeacrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleicacid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid. Specific examples of the unsaturated sulfonic acidmonomer include styrene sulfonic acid, 2-acrylamido-2-methyl propanesulfonic acid, 3-sulfopropyl (meth)acrylate, andbis-(3-sulfopropyl)-itaconate. Specific examples of the unsaturatedphosphoric acid monomer include vinyl phosphoric acid, vinyl phosphate,bis(methacryloxyethyl)phosphate, diphenyl-2-acryloyloxyethyl phosphate,diphenyl-2-methacryloyloxyethyl phosphate, anddibutyl-2-acryloyloxyethyl phosphate.

The latex binder polymer particles preferably have a glass transitiontemperature (Tg) of 30° C. or more.

The minimum film-forming temperature (MFT) of the polymer latex ispreferably −25 to 150° C., and more preferably 35 to 130° C.

Biocides

Suitable biocides for the aqueous inkjet inks include sodiumdehydroacetate, 2-phenoxyethanol, sodium benzoate, sodiumpyridinethion-1-oxide, ethyl p-hydroxybenzoate and1,2-benzisothiazolin-3-one and salts thereof.

Preferred biocides are Proxel™ GXL and Proxel™ Ultra 5 available fromARCH UK BIOCIDES and Bronidox™ available from COGNIS.

A biocide is preferably added in an amount of 0.001 to 3.0 wt. %, morepreferably 0.01 to 1.0 wt. %, each based on the total weight of thepigmented inkjet ink.

Humectants

Suitable humectants include triacetin, N-methyl-2-pyrrolidone,2-pyrrolidone, glycerol, urea, thiourea, ethylene urea, alkyl urea,alkyl thiourea, dialkyl urea and dialkyl thiourea, diols, includingethanediols, propanediols, propanetriols, butanediols, pentanediols, andhexanediols; glycols, including propylene glycol, polypropylene glycol,ethylene glycol, polyethylene glycol, diethylene glycol, tetraethyleneglycol, and mixtures and derivatives thereof. Preferred humectants are2-pyrrolidone, glycerol and 1,2-hexanediol, since the latter were foundto be the most effective for improving inkjet printing reliability in anindustrial environment.

The humectant is preferably added to the inkjet ink formulation in anamount of 0.1 to 35 wt % of the formulation, more preferably 1 to 30 wt% of the formulation, and most preferably 3 to 25 wt % of theformulation.

pH Adjusters

The aqueous inkjet inks may contain at least one pH adjuster. SuitablepH adjusters include NaOH, KOH, NEt₃, NH₃, HCl, HNO₃, H₂SO₄ and(poly)alkanolamines such as triethanolamine and2-amino-2-methyl-1-propaniol. Preferred pH adjusters are triethanolamine, NaOH and H₂SO₄.

Surfactants

The one or more aqueous inkjet inks may contain at least one surfactant.The surfactant(s) can be anionic, cationic, non-ionic, or zwitter-ionicand are usually added in a total quantity less than 5 wt % based on thetotal weight of the inkjet ink and particularly in a total less than 2wt % based on the total weight of the inkjet ink.

The one or more aqueous inkjet inks preferably have a surface tensionbetween 18.0 and 45.0 mN/m at 25° C., more preferably between a surfacetension between 21.0 and 39.0 mN/m at 25° C.

Suitable surfactants for the aqueous inkjet inks include fatty acidsalts, ester salts of a higher alcohol, alkylbenzene sulphonate salts,sulphosuccinate ester salts and phosphate ester salts of a higheralcohol (for example, sodium dodecylbenzenesulphonate and sodiumdioctylsulphosuccinate), ethylene oxide adducts of a higher alcohol,ethylene oxide adducts of an alkylphenol, ethylene oxide adducts of apolyhydric alcohol fatty acid ester, and acetylene glycol and ethyleneoxide adducts thereof (for example, polyoxyethylene nonylphenyl ether,and SURFYNOL™ 104, 104H, 440, 465 and TG available from AIR PRODUCTS &CHEMICALS INC.).

Preferred surfactants are selected from fluoro surfactants (such asfluorinated hydrocarbons) and/or silicone surfactants.

The silicone surfactants are preferably siloxanes and can bealkoxylated, polyester modified, polyether modified, polyether modifiedhydroxy functional, amine modified, epoxy modified and othermodifications or combinations thereof. Preferred siloxanes arepolymeric, for example polydimethylsiloxanes. Preferred commercialsilicone surfactants include BYK™ 333 and BYK™ UV3510 from BYK Chemie.

A particularly preferred commercial fluorosurfactant is Capstone™ FS3100from DU PONT.

Preparation of Inkjet Inks

The one or more aqueous inkjet inks may be prepared by precipitating ormilling the colour pigment in the dispersion medium in the presence ofthe polymeric dispersant, or simply by mixing a self-dispersible colourpigment in the ink.

Mixing apparatuses may include a pressure kneader, an open kneader, aplanetary mixer, a dissolver, and a Dalton Universal Mixer. Suitablemilling and dispersion apparatuses are a ball mill, a pearl mill, acolloid mill, a high-speed disperser, double rollers, a bead mill, apaint conditioner, and triple rollers. The dispersions may also beprepared using ultrasonic energy.

If the inkjet ink contains more than one pigment, the colour ink may beprepared using separate dispersions for each pigment, or alternativelyseveral pigments may be mixed and co-milled in preparing the dispersion.

The dispersion process can be carried out in a continuous, batch orsemi-batch mode.

The preferred amounts and ratios of the ingredients of the mill grindwill vary widely depending upon the specific materials and the intendedapplications. The contents of the milling mixture comprise the millgrind and the milling media. The mill grind comprises pigment,dispersant and a liquid carrier such as water. For aqueous ink-jet inks,the pigment is usually present in the mill grind at 1 to 50 wt %,excluding the milling media. The weight ratio of pigment over dispersantis 20:1 to 1:2.

The milling time can vary widely and depends upon the pigment,mechanical means and residence conditions selected, the initial anddesired final particle size, etc. In the present invention pigmentdispersions with an average particle size of less than 100 nm may beprepared.

After milling is completed, the milling media is separated from themilled particulate product (in either a dry or liquid dispersion form)using conventional separation techniques, such as by filtration, sievingthrough a mesh screen, and the like. Often the sieve is built into themill, e.g. for a bead mill. The milled pigment concentrate is preferablyseparated from the milling media by filtration.

In general it is desirable to make the colour ink in the form of aconcentrated mill grind, which is subsequently diluted to theappropriate concentration for use in the ink-jet printing system. Thistechnique permits preparation of a greater quantity of pigmented inkfrom the equipment. If the mill grind was made in a solvent, it isdiluted with water and optionally other solvents to the appropriateconcentration. If it was made in water, it is diluted with eitheradditional water or water miscible solvents to make a mill grind of thedesired concentration. By dilution, the ink is adjusted to the desiredviscosity, colour, hue, saturation density, and print area coverage forthe particular application.

Decorative Surfaces

The decorative surfaces are preferably rigid or flexible panels, but mayalso be rolls of a flexible substrate. In a preferred embodiment thedecorative panels are selected from the group consisting of kitchenpanels, flooring panels, furniture panels, ceiling panels and wallpanels.

A decorative panel (30), illustrated by a flooring panel having also atongue and groove join (33, 32) in FIG. 3, includes preferably at leasta core layer (31) and a decorative layer (34). In order to protect thecolour pattern of the decorative layer (34) against wear, a protectivelayer (35) may be applied on top of the decorative layer (34). Abalancing layer (36) may also be applied at the opposite side of thecore layer (31) to restrict or prevent possible bending of thedecorative panel (30). The assembly into a decorative panel of thebalancing layer, the core layer, the decorative layer, and preferablyalso a protective layer, is preferably performed in the same presstreatment of preferably a DPL process (Direct Pressure Laminate).

In a preferred embodiment of decorative panels, tongue and grooveprofiles (33 respectively 32 in FIG. 3) are milled into the side ofindividual decorative panels which allow them to be slid into oneanother. The tongue and grove join ensures, in the case of flooringpanels, a sturdy floor construction and protects the floor, preventingdampness from penetrating.

In a more preferred embodiment, the decorative panels include a tongueand a groove of a special shape (e.g. 33 respectively 32 in FIG. 4)which allow them to be clicked into one another. The advantage thereofis an easy assembly requiring no glue. The shape of the tongue andgroove necessary for obtaining a good mechanical join is well-known inthe art of laminate flooring, as also exemplified in EP 2280130 A(FLOORING IND), WO 2004/053258 (FLOORING IND), US 2008010937 (VALINGE)and U.S. Pat. No. 6,418,683 (PERSTORP FLOORING).

The tongue and groove profiles are especially preferred for flooringpanels and wall panels, but in the case of furniture panels, such tongueand groove profile is preferably absent for aesthetical reasons of thefurniture doors and drawer fronts. However, a tongue and groove profilemay be used to click together the other panels of the furniture, asillustrated by US 2013071172 (UNILIN).

The decorative surfaces, especially decorative panels, may furtherinclude a sound-absorbing layer as disclosed by U.S. Pat. No. 8,196,366(UNILIN).

In a preferred embodiment, the decorative panel is an antistatic layeredpanel. Techniques to render decorative panels antistatic are well-knownin the art of decorative surfaces as exemplified by EP 1567334 A(FLOORING IND).

The top surface of the decorative surface, i.e. at least the protectivelayer, is preferably provided with a relief matching the colour pattern,such as for example the wood grain, cracks and nuts in a woodprint.Embossing techniques to accomplish such relief are well-known anddisclosed by, for example, EP 1290290 A (FLOORING IND), US 2006144004(UNILIN), EP 1711353 A (FLOORING IND) and US 2010192793 (FLOORING IND).

In a preferred embodiment, the decorative panels are made in the form ofrectangular oblong strips. The dimensions thereof may vary greatly.Preferably the panels have a length exceeding 1 meter, and a widthexceeding 0.1 meter, e.g. the panels can be about 1.3 meter long andabout 0.15 meter wide. According to a special preferred embodiment thelength of the panels exceeds 2 meter, with the width being preferablyabout 0.2 meter or more. The print of such panels is preferably freeform repetitions.

Core Layers

The core layer is preferably made of wood-based materials, such asparticle board, MDF or HDF (Medium Density Fibreboard or High DensityFibreboard), Oriented Strand Board (OSB) or the like. Also, use can bemade of boards of synthetic material or boards hardened by means ofwater, such as cement boards. In a particularly preferred embodiment,the core layer is a MDF or HDF board.

The core layer may also be assembled at least from a plurality of papersheets, or other carrier sheets, impregnated with a thermosetting resinas disclosed by WO 2013/050910 (UNILIN). Preferred paper sheets includeso-called Kraft paper obtained by a chemical pulping process also knownas the Kraft process, e.g. as described in U.S. Pat. No. 4,952,277 (BETPAPERCHEM).

In another preferred embodiment, the core layer is a board materialcomposed substantially of wood fibres which are bonded by means of apolycondensation glue, wherein the polycondensation glue forms 5 to 20percent by weight of the board material and the wood fibres are obtainedfor at least 40 percent by weight from recycled wood. Suitable examplesare disclosed by EP 2374588 A (UNILIN).

Instead of a wood based core layer, also a synthetic core layer may beused, such as those disclosed by US 2013062006 (FLOORING IND). In apreferred embodiment, the core layer comprises a foamed syntheticmaterial, such as foamed polyethylene or foamed polyvinyl chloride.

Other preferred core layers and their manufacturing are disclosed by US2011311806 (UNILIN) and U.S. Pat. No. 6,773,799 (DECORATIVE SURFACES).

The thickness of the core layer is preferably between 2 and 12 mm, morepreferably between 5 and 10 mm.

Paper Substrates

The decorative layer and preferably, if present also the protectivelayer and/or balancing layer, include paper as substrate.

The paper preferably has a weight of less than 150 g/m², because heavierpaper sheets are hard to impregnate all through their thickness with athermosetting resin. Preferably said paper layer has a paper weight,i.e. without taking into account the resin provided on it, of between 50and 100 g/m² and possibly up to 130 g/m². The weight of the paper cannotbe too high, as then the amount of resin needed to sufficientlyimpregnate the paper would be too high, and reliably further processingthe printed paper in a pressing operation becomes badly feasible.

Preferably, the paper sheets have a porosity according to Gurley'smethod (DIN 53120) of between 8 and 20 seconds. Such porosity allowseven for a heavy sheet of more than 150 g/m² to be readily impregnatedwith a relatively high amount of resin.

Suitable paper sheets having high porosity and their manufacturing arealso disclosed by U.S. Pat. No. 6,709,764 (ARJO WIGGINS).

The paper for the decorative layer is preferably a white paper and mayinclude one or more whitening agents, such as titanium dioxide, calciumcarbonate and the like. The presence of a whitening agent helps to maskdifferences in colour on the core layer which can cause undesired coloureffects on the colour pattern.

Alternatively, the paper for the decorative layer is preferably a bulkcoloured paper including one or more colour dyes and/or colour pigments.Besides the masking of differences in colour on the core layer, the useof a coloured paper reduces the amount of inkjet ink required to printthe colour pattern. For example, a light brown or grey paper may be usedfor printing a wood motif as colour pattern in order to reduce theamount of inkjet ink needed.

In a preferred embodiment, unbleached Kraft paper is used for a brownishcoloured paper in the decorative layer. Kraft paper has a low lignincontent resulting in a high tensile strength. A preferred type of Kraftpaper is absorbent Kraft paper of 40 to 135 g/m² having a high porosityand made from clean low kappa hardwood Kraft of good uniformity.

If the protective layer includes a paper, then a paper is used whichbecomes transparent or translucent after resin impregnation so that forthe colour pattern in the decorative layer can be viewed.

The above papers may also be used in the balancing layer.

It was found in the present invention that no special ink receivinglayer or substance was necessary for obtaining good image quality.Hence, the paper is preferably free of any separate ink receiving layerupon printing.

For the sake of clarity, it should be clear that resin coated papers,so-called RC papers, are not the thermosetting resin impregnated papersof the manufacturing method according to the invention. The RC papersused in home/office aqueous inkjet printing consist of a porous papercore free of resin. The RC papers have only on their surface a resincoating, usually a polyethylene or polypropylene resin coating, withthereon one or more ink receiving layers, usually containing ahydrophilic polymer like polyvinylalcohol and optionally porous pigmentslike fumed silica. Such RC papers have a low permeability for thethermosetting resin leading to inhomogeneous resin absorption and higherrisk for delamination after pressing.

Thermosetting Resins

The thermosetting resin is preferably selected from the group consistingof melamine-formaldehyde based resins, ureum-formaldehyde based resinsand phenol-formaldehyde based resins.

Other suitable resins for impregnating the paper are listed in [0028] ofEP 2274485 A (HUELSTA).

Most preferably the thermosetting resin is a melamine-formaldehyde basedresin, often simply referred to in the art as a ‘melamine (based)resin’.

The melamine formaldehyde resin preferably has a formaldehyde tomelamine ratio of 1.4 to 2. Such melamine based resin is a resin thatpolycondensates while exposed to heat in a pressing operation. Thepolycondensation reaction creates water as a by-product. It isparticularly with these kinds of thermosetting resins, namely thosecreating water as a by-product, that the present invention is ofinterest. The created water, as well as any water residue in thethermosetting resin before the pressing, must leave the hardening resinlayer to a large extent before being trapped and leading to a loss oftransparency in the hardened layer. The available ink layer can hinderthe diffusion of the vapour bubbles to the surface, however the presentinvention provides measures for limiting such hindrance.

The paper is preferably provided with an amount of thermosetting resinequalling 40 to 250% dry weight of resin as compared to weight of thepaper. Experiments have shown that this range of applied resin providesfor a sufficient impregnation of the paper, that avoids splitting to alarge extent, and that stabilizes the dimension of the paper to a highdegree.

The paper is preferably provided with such an amount of thermosettingresin, that at least the paper core is satisfied with the resin. Suchsatisfaction can be reached when an amount of resin is provided thatcorresponds to at least 1.5 or at least 2 times the paper weight.Preferably the paper is firstly impregnated through or satisfied, and,afterwards, at least at the side thereof to be printed, resin ispartially removed.

Preferably the resin provided on said paper is in a B-stage whileprinting. Such B-stage exists when the thermosetting resin is notcompletely cross linked.

Preferably the resin provided on said paper has a relative humiditylower than 15%, and still better of 10% by weight or lower whileprinting.

Preferably the step of providing said paper with thermosetting resininvolves applying a mixture of water and the resin on the paper. Theapplication of the mixture might involve immersion of the paper in abath of the mixture and/or spraying or jetting the mixture. Preferablythe resin is provided in a dosed manner, for example by using one ormore squeezing rollers and/or doctor blades to set the amount of resinadded to the paper layer.

Methods for impregnating a paper substrate with resin are well-known inthe art as exemplified by WO 2012/126816 (VITS) and EP 966641 A (VITS).

The dry resin content of the mixture of water and resin for impregnationdepends on the type of resin. An aqueous solution containing aphenol-formaldehyde resin preferably has a dry resin content of about30% by weight, while an aqueous solution containing amelamine-formaldehyde resin preferably has a dry resin content of about60% by weight. Methods of impregnation with such solutions are disclosedby e.g. U.S. Pat. No. 6,773,799 (DECORATIVE SURFACES).

The paper is preferably impregnated with the mixtures known from U.S.Pat. No. 4,109,043 (FORMICA CORP) and U.S. Pat. No. 4,112,169 (FORMICACORP), and hence preferably comprise, next to melamine formaldehyderesin, also polyurethane resin and/or acrylic resin.

The mixture including the thermosetting resin may further includeadditives, such as colorants, surface active ingredients, biocides,antistatic agents, hard particles for wear resistance, elastomers, UVabsorbers, organic solvents, acids, bases, and the like.

The advantage of adding a colorant to the mixture containing thethermosetting resin is that a single type of white paper can be used formanufacturing the decorative layer, thereby reducing the stock of paperfor the decorative laminate manufacturer. The use of a colored paper, asalready described above, to reduce the amount of ink required forprinting a wood motif, is here accomplished by the white paper beingcolored by impregnation by a brownish thermosetting resin. The latterallows a better control of the amount of brown colour required forcertain wood motifs.

Antistatic agents may be used in thermosetting resin. However preferablyantistatic agents, like NaCl and KCl, carbon particles and metalparticles, are absent in the resin, because often they have undesiredside effects such as a lower water resistance or a lower transparency.Other suitable antistatic agents are disclosed by EP 1567334 A (FLOORINGIND).

Hard particles for wear resistance are preferably included in aprotective layer.

Decorative Layers

The decorative layer includes a thermosetting resin impregnated paperand a colour pattern printed thereon by inkjet. In the assembleddecorative panel, the colour pattern is located on the resin impregnatedpaper on the opposite side than the side facing the core layer.

Before printing a colour pattern, or at least a portion thereof, thepaper that has been provided with resin. This measure improves thestability of the paper. In such cases at least a portion of theexpansion or shrinkage due to the resin provision takes place beforeinkjet printing. Preferably the resin provided paper is dried beforeinkjet printing, for example to a residual humidity of 10% or less. Inthis case the most important portion of the expansion or shrinkage ofthe paper layer is neutralized. The advantage of having this dimensionalstability is especially observed in the cases where, like in EP 1290290A (FLOORING IND), a correspondence between the relief and the printeddecor is desired.

A decorative panel, like a floor panel, has on one side of the corelayer a decorative layer and a balancing layer on the other side of thecore layer. However, a decorative layer may be applied on both sides ofthe core layer. The latter is especially desirable in the case oflaminate panels for furniture. In such a case, preferably also aprotective layer is applied on both decorative layers present on bothsides of the core layer.

Colour Patterns

The colour pattern is obtained by jetting and drying one or more aqueousinkjet inks of an aqueous inkjet ink set upon on a thermosetting resinimpregnated paper, wherein said one or more aqueous inkjet inks includea polymer latex binder.

The colour pattern represents preferably less than 6 g/m² ink, morepreferably less than 5 g/m² ink, and most preferably between 1.2 and 4.0g/m² ink as dry weight.

There is no real restriction on the content of the colour pattern. Thecolour pattern may also contain information such as text, arrows, logo'sand the like. The advantage of inkjet printing is that such informationcan be printed at low volume without extra cost, contrary to gravureprinting.

In a preferred embodiment, the colour pattern is a wood reproduction ora stone reproduction, but it may also be a fantasy or creative pattern,such as an ancient world map or a geometrical pattern, or even a singlecolour for making, for example, a floor consisting of black and redtiles or a single colour furniture door.

An advantage of printing a wood colour pattern is that a floor can bemanufactured imitating besides oak, pine and beech, also very expensivewood like black walnut which would normally not be available for housedecoration.

An advantage of printing a stone colour pattern is that a floor can bemanufactured which is an exact imitation of a stone floor, but withoutthe cold feeling when walking barefooted on it.

Protective Layers

Preferably a further resin layer, a protective layer, is applied abovethe printed pattern after printing, e.g. by way of an overlay, i.e. aresin provided carrier, or a liquid coating, preferably while the decorlayer is laying on the substrate, either loosely or already connected oradhered thereto.

In a preferred embodiment, the carrier of the overlay is a paperimpregnated by a thermosetting resin that becomes transparent ortranslucent after heat pressing in a DPL process.

A preferred method for manufacturing such an overlay is described in US2009208646 (DEKOR-KUNSTSTOFFE).

The liquid coating includes preferably a thermosetting resin, but mayalso be another type of liquid such as a UV- or an EB-curable varnish.

In a particularly preferred embodiment, the liquid coating includes amelamine resin and hard particles, like corundum.

The protective layer is preferably the outermost layer, but in anotherpreferred embodiment a thermoplastic or elastomeric surface layer may becoated on the protective layer, preferably of pure thermoplastic orelastomeric material. In the latter case, preferably a thermoplastic orelastomeric material based layer is also applied on the other side ofthe core layer.

Liquid melamine coatings are exemplified in DE 19725829 C (LSINDUSTRIELACKE) and U.S. Pat. No. 3,173,804 (RENKL PAIDIWERK).

The liquid coating may contain hard particles, preferably transparenthard particles. Suitable liquid coatings for wear protection containinghard particles and methods for manufacturing such a protective layer aredisclosed by US 2011300372 (CT FOR ABRASIVES AND REFRACTORIES) and U.S.Pat. No. 8,410,209 (CT FOR ABRASIVES AND REFRACTORIES).

The transparency and also the colour of the protective layer can becontrolled by the hard particles, when they comprise one or a pluralityof oxides, oxide nitrides or mixed oxides from the group of elements Li,Na, K, Ca, Mg, Ba, Sr, Zn, Al, Si, Ti, Nb, La, Y, Ce or B.

The total quantity of hard particles and transparent solid materialparticles is typically between 5% by volume and 70% by volume, based onthe total volume of the liquid coating. The total quantity of hardparticles is between 1 g/m² and 100 g/m², preferably 2 g/m² to 50 g/m².

If the protective layer includes a paper as carrier sheet for thethermosetting resin, then the hard particles, such as aluminium oxideparticles, are preferably incorporated in or on the paper. Preferredhard particles are ceramic or mineral particles chosen from the group ofaluminium oxide, silicon carbide, silicon oxide, silicon nitride,tungsten carbide, boron carbide, and titanium dioxide, or from any othermetal oxide, metal carbide, metal nitride or metal carbonitride. Themost preferred hard particles are corundum and so-called Sialonceramics. In principle, a variety of particles may be used. Of course,also any mixture of the above-mentioned hard particles may be applied.

In an alternative preferred embodiment of a protective layer including apaper as carrier sheet for the thermosetting resin, the inkjet printingis performed on the thermosetting resin impregnated paper of theprotective layer. The other paper substrate including a whitening agent,such as titanium dioxide, may then merely be used to mask surfacedefects of the core layer.

The amount of hard particles in the protective layer may determined infunction of the desired wear resistance, preferably by a so-called Tabertest as defined in EN 13329 and also disclosed in WO 2013/050910 A(UNILIN) and U.S. Pat. No. 8,410,209 (CT FOR ABRASIVES AND REFRACTOR).

Hard particles having an average particle size of between 1 and 200 μmare preferred. Preferably an amount of such particles of between 1 and40 g/m² is applied above the printed pattern. An amount lower than 20g/m² can suffice for the lower qualities.

If the protective layer includes a paper, then it preferably has a paperweight of between 10 and 50 g/m². Such a paper is often also referred toas a so-called overlay commonly used in laminate panels. Preferredmethods for manufacturing such an overlay are disclosed by WO2007/144718 (FLOORING IND).

Preferably the step of providing the protective layer of thermosettingresin above the printed pattern involves a press treatment. Preferably atemperature above 150° C. is applied in the press treatment, morepreferably between 180° and 220° C., and a pressure of more than 20 bar,more preferably between 35 and 40 bar.

In a very preferred embodiment, the decorative panel is manufacturedusing two press treatments, because this results in an extremely highabrasion resistance. Indeed, during the first press treatment,preferably the layers immediately underlying the wear resistantprotective layer are substantially or wholly cured. The hard particlescomprised in the wear resistant protective layer are thereby preventedfrom being pushed down out of the top area of the floor panel into thecolour pattern or below the colour pattern and stay in the zone wherethey are most effective, namely essentially above the colour pattern.This makes it possible to reach an initial wear point according to theTaber test as defined in EN 13329 of over 10000 rounds, where in onepress treatment of layers with the same composition only just over 4000rounds were reached. It is clear that the use of two press treatments asdefined above, leads to a more effective use of available hardparticles. An alternative advantage of using at least two presstreatments lays in the fact that a similar wearing rate, as in the casewhere a single press treatment is used, can be obtained with less hardparticles if the product is pressed twice. Lowering the amount of hardparticles is interesting, since hard particles tend to lower thetransparency of the wear resistant protective layer, which isundesirable. It becomes also possible to work with hard particles ofsmaller diameter, e.g. particles having an average particle diameter of15 μm or less, or even of 5 μm or less.

Balancing Layers

The main purpose of the balancing layer(s) is to compensate tensileforces by layers on the opposite side of the core layer, so that anessentially flat decorative panel is obtained. Such a balancing layer ispreferably a thermosetting resin layer, that can comprise one or morecarrier layers, such as paper sheets.

As already explained above for a furniture panel, the balancing layer(s)may be a decorative layer, optionally complemented by a protectivelayer.

Instead of one or more transparent balancing layers, also an opaquebalancing layer may be used which gives the decorative panel a moreappealing look by masking surface irregularities. Additionally, it maycontain text or graphical information such as a company logo or textinformation.

Inkjet Printing Devices

The one or more aqueous inkjet inks, including the polymer latex binder,may be jetted by one or more print heads ejecting small droplets in acontrolled manner through nozzles onto a substrate, which is movingrelative to the print head(s).

A preferred print head for the inkjet printing system is a piezoelectrichead. Piezoelectric inkjet printing is based on the movement of apiezoelectric ceramic transducer when a voltage is applied thereto. Theapplication of a voltage changes the shape of the piezoelectric ceramictransducer in the print head creating a void, which is then filled withink. When the voltage is again removed, the ceramic expands to itsoriginal shape, ejecting a drop of ink from the print head. However themanufacturing method according to the present invention is notrestricted to piezoelectric inkjet printing. Other inkjet print headscan be used and include various types, such as a continuous type.

The inkjet print head normally scans back and forth in a transversaldirection across the moving ink-receiver surface. Often the inkjet printhead does not print on the way back. Bi-directional printing ispreferred for obtaining a high area throughput. Another preferredprinting method is by a “single pass printing process”, which can beperformed by using page wide inkjet print heads or multiple staggeredinkjet print heads which cover the entire width of the ink-receiversurface. In a single pass printing process the inkjet print headsusually remain stationary and the substrate surface is transported underthe inkjet print heads.

EXAMPLES Materials

All materials used in the following examples were readily available fromstandard sources such as Aldrich Chemical Co. (Belgium) and Acros(Belgium) unless otherwise specified.

PB15:3 is an abbreviation used for Hostaperm™ B4G-KR, a C.I. PigmentBlue 15:3 pigment from CLARIANT.

PR254 is the abbreviation for C.I. Pigment Red 254 for which Irgazin™DPP Red BTR from Ciba Specialty Chemicals was used.

PY151 is an abbreviation used for INK JET H4G LV 3853, a C.I. PigmentYellow 151 from CLARIANT.

PBL7 is an abbreviation used for Printex™ 90, a carbon black pigmentfrom EVONIK.

Edaplan is an abbreviation used for Edaplan™ 482, a polymeric dispersantfrom MUNZING.

Proxel is an abbreviation used for the biocide Proxel™ Ultra 5 fromAVECIA.

PEG 200 is a polyethylene glycol having an average molecular mass of 200from CLARIANT.

PEG 600 is a polyethylene glycol having an average molecular weightbetween 570 and 630 g/mol from CALDIC BELGIUM nv.

TEA is triethanol amine.

PY139 is Graphtol™ Yellow H2R VP2284, a C.I. Pigment Yellow 139 fromCLARIANT.

PY110 is IRGAZIN™ YELLOW L 2040, a C.I. Pigment Yellow 110 from BASF.

PY120 is NOVOPERM™ YELLOW H2G, a C.I. Pigment Yellow 120 from CLARIANT.

PY128 is CROMOPHTAL™ JET YELLOW 8GT, a C.I. Pigment Yellow 128 fromBASF.

PY73 is HANSA™ BRILLIANT YELLOW 4GX, a C.I. Pigment Yellow 73 fromCLARIANT.

PY154 is HOSTAPERM™ YELLOW H3G, a C.I. Pigment Yellow 154 from CLARIANT.

PY55 is SEIKAFAST™ YELLOW 2500, a C.I. Pigment Yellow 55 fromDainichiseika Colour & Chemicals Mfg. Co.

PY97 is Novoperm™ Yellow FGL, a C.I. Pigment Yellow 97 from CLARIANT.

PY17 is GRAPHTOL™ YELLOW GG, a C.I. Pigment Yellow 17 from CLARIANT.

PY138 is Paliotol™ Yellow D0960, a C.I. Pigment Yellow 138 from BASF.

Cab-O-Jet™ 450C is a 15% dispersion of C.I. Pigment Blue 15:4 in waterhaving an average particle size of 115 nm.

Cab-O-Jet™ 465M is a 15% dispersion of C.I. Pigment Red 122 in waterhaving an average particle size of 100 nm.

Cab-O-Jet™ 470Y is a 15% dispersion of C.I. Pigment Yellow 74 in waterhaving an average particle size of 170 nm.

Cab-O-Jet™ 300 is a 15% dispersion of C.I. Pigment Black 7 in waterhaving an average particle size of 130 nm.

D75C is a 15% dispersion of C.I. Pigment Blue 15:3 in water having asurface tension of 55 mN/m and an average particle size of 100 nm.

D71M is a 15% dispersion of C.I. Pigment Red 122 in water having asurface tension of 50 mN/m and an average particle size of 145 nm.

D75Y is a 15% dispersion of C.I. Pigment Yellow 74 in water having asurface tension of 55 mN/m and an average particle size of 100 nm.

D73K is a 15% dispersion of C.I. Pigment Black 7 in water having asurface tension of 55 mN/m and an average particle size of 105 nm.

Emuldur™ 381A is a 40% solids latex dispersion in water of apolyester-polyurethane polymer having a glass transition temperature of30° C.

Capstone™ FS3100 is a fluorosurfactant from DU PONT.

MH is a 120 g/m² matt coated paper available as MH 1281 from MITSUBISHI.

Measurement Methods

1. CIELAB Parameters

The reflectance spectrum of each sample was measured three times with aGretag SPM50 spectrophotometer in the range from 380 up to 730 nm insteps of 10 nm.

Unless otherwise specified, the CIE L* a* b* coordinates as well aschroma C* and hue angle H* were calculated for a 2° observer and a D50light source.

2. Metameric Index MI

Metamerism is a phenomenon which occurs when two materials match incolour under some lighting conditions but not under other lightingconditions. A customer expects all parts of e.g. a kitchen cabinet thatare the same colour to match whether viewed in daylight, under halogenlighting or under Neon lighting.

In the CIELAB colour space, a colour is defined using three terms L*,a*, and b*. L* defines the lightness of a colour, and it ranges fromzero (black) to 100 (white). The terms a* and b*, together, define thehue. The term a* ranges from a negative number (green) to a positivenumber (red). The term b* ranges from a negative number (blue) to apositive number (yellow). Additional terms such as hue angle H* andchroma C* are used to further describe a given colour, wherein:H*=tan⁻¹(b*/a*)  equation 1C*=(a* ² +b* ²)^(1/2)  equation 2.

In the CIELAB colour space, ΔE* defines the “colour-distance”, i.e. thedifference between two colours, such as the colour of the originalprinted image and the colour of the same image after light fading. Thehigher the ΔE* number, the more difference between the two colours:ΔE*=(ΔL* ² +Δa* ² +Δb* ²)^(1/2)  equation 3.The CIE 1994 Colour Difference Model provided an improved calculation ofthe colour difference by including some weighing factors. The colourdifference measured under the new model is indicated by ΔE94.

$\begin{matrix}{{{\Delta\; E_{94}^{*}} = \sqrt{\left( \frac{\Delta\; L^{*}}{K_{L}} \right)^{2} + \left( \frac{\Delta\; C^{*}}{1 + {K_{1}C_{1}^{*}}} \right)^{2} + \left( \frac{\Delta\; H^{*}}{1 + {K_{2}C_{1}^{*}}} \right)^{2}}},} & {{equation}\mspace{14mu} 4}\end{matrix}$wherein:ΔL*=L ₁ *−L ₂ *,C ₁*=√{square root over (a ₁*² +b ₁*²)}, C ₂*=√{squareroot over (a ₂*² +b ₂*²)},ΔC*=C ₁ *−C ₂ *,Δa*=a ₁ *−a ₂ *,Δb*=b ₁ *−b ₂* andΔH*=√{square root over (ΔE* ² −ΔL* ² −ΔC* ²)}=√{square root over (Δa* ²+Δb* ² −ΔC* ²)}and where the weighting factors depend on the application. Fordecoration applications: K_(L)=1, K₁=0.045 and K₂=0.015.

For metamerism, two materials are considered. For example, in case ofdeco printing of wood colours, the first (or reference) material couldbe a piece of natural wood of some kind or a kitchen cabinet door,produced with rotogravure techniques. The second material may be thebest possible reproduction of that first material by means of inkjetprinting.

The reflectance spectrum of both materials is calculated for a selectedset of light sources out of a list of 19 light sources:

-   -   Equi-energetic light source: CIE illuminant E    -   Daylight: D50, D55, D65    -   CIE standard illuminants: A (tungsten filament), B (direct        daylight), C (shady daylight)    -   Fluorescent: CIE F-series F1 up to F12

The reflectance spectrum of each sample was measured three times with aGretag SPM50 spectrophotometer in the range from 380 up to 730 nm insteps of 10 nm. Calculation involved the reflectance spectrum of thematerial in combination with the light source spectrum. The CIE L* b*coordinates for a 2° observer as well as chroma C* and hue angle H* werecalculated for each material and for each light source.

For each light source, the difference values for ΔL*, Δa*, Δb*, ΔC*, ΔH*and the colour-distance ΔE*94 were calculated for the two materials,i.e. the reference material and the printed material, which thusdelivered 19 sets of difference values for each reference sample andinkjet printed material. Simple descriptive statistics on the 19 sets ofdifference values was calculated.

The metameric index for the 2 materials was defined as three times thestandard deviation of ΔE*94. The smaller the metameric index, the lesscolour difference between the 2 materials will be seen when they arecompared to each other whilst changing light source within the selectedset of 19 light sources. For a true reproduction of wood colours havingminimal metamerism, the metameric index should have a value of no morethan 1.0.

3. Surface Tension

The static surface tension of the aqueous inkjet inks was measured witha KRÜSS tensiometer K9 from KRÜSS GmbH, Germany at 25° C. after 60seconds.

4. Viscosity

The viscosity of an inkjet ink was measured, using a Brookfield DV-II+viscometer at 32° C. at a shear rate of 1,000 s⁻¹.

5. Average Particle Size

An ink sample is diluted with ethyl acetate to a pigment concentrationof 0.002 wt %. The average particle size of pigment particles isdetermined with a Nicomp™ 30 Submicron Particle Analyzer based upon theprinciple of dynamic light scattering.

For good ink jet characteristics (jetting and print quality) the averageparticle size of the dispersed particles is preferably below 250 nm.

6. Ink Stability

The inkjet ink is considered to be a stable pigment dispersion if theaverage particle size did not increase by more than 15% after a heattreatment of 7 days at 60° C.

The inkjet ink is considered to be a stable pigment dispersion if theviscosity did not increase by more than 10% after a heat treatment of 7days at 60° C.

7. Lightfastness

The lightfastness was determined as the colour hue shift ΔE94* between aprint sample measured one hour after printing and the same print after 1week exposure to Xenon light in a Atlas Xenotest™ 150S at an irradianceof 300-800 nm at 1250 W/m2 performed indoor behind window glass.

A colour hue change ΔE94*-value of 1.0 is clearly visible to the nakedeye.

8. Blue Wool Scale

The Blue Wool Scale was used as a measure of lightfastness of inkjetprinted samples. The test originates from the textile industry, but hasbeen adopted by the laminate flooring industry (see e.g. the websiteww.eplf.com from the European Producers of Laminate Flooring).

Two identical samples were made. One was placed in the dark as thecontrol and the other was placed in the equivalent of sunlight for athree-month period. A standard blue wool textile fading test cardconform to the ISO 105-b01 standard was also placed in the same lightconditions as the sample under test. The amount of fading of the samplewas then assessed by comparison to the original colour.

A rating between 0 and 8 is awarded by identifying which one of theeight strips on the blue wool standard card has faded to the same extentas the sample under test. Zero denotes extremely poor colour fastnesswhilst a rating of eight is deemed not to have altered from the originaland thus credited as being lightfast and permanent.

The flooring industry expects a laminate floor to have a rating on theblue wool scale of 6 or more.

9. Latency

Latency is the time that nozzles can be left uncovered and idle beforethere is a significant reduction in performance, for instance areduction in drop velocity that will noticeably affect the image qualityor even failing nozzles which no longer eject the ink.

Prints were made using a KJ4B Kyocera print head at a head temperatureof 32° C. at 600 dpi on a glossy microporous paper after having left thenozzles uncovered and idle for 10 minutes, 20 minutes, 30 minutes and 60minutes. An evaluation was made of the image quality on the printedsample by checking failing nozzles and image unevenness.

If no negative effect was observed at 60 minutes, then the latency wasconsidered to be more than 60 minutes. Alternatively, if after 10minutes no good image quality was observed, the latency was consideredto be less than 10 minutes. An intermediate latency was observed between10 and 60 minutes, the longer the open head time could be, the betterthe latency. A latency of more than 30 minutes is desirable.

10. Adhesion

Adhesion is evaluated by a cross-cut test according to ISO2409:1992(E).Paints. International standard. 1992-08-15. using a Braive No. 1536Cross Cut Tester from BRAIVE INSTRUMENTS with spacing of a 1 mm betweencuts and using a weight of 600 g, in combination with a Tesatape™ 4104PVC tape. The evaluation was made in accordance with a criteriondescribed by Table 1.

TABLE 1 Criterion Observation 0 The edges of the cuts are completelysmooth: none of the squares of the lattice is detached (=perfectadhesion). 1 Detachment of small flakes at the intersections of thecuts. A cross-cut area not greater than 5% is affected. 2 Flaked alongthe edges and/or at the intersections of the cuts. A cross-cut areagreater than 5%, but not significantly greater than 15%, is affected. 3Flaked along the edges of the cuts partly or wholly in large ribbons,and/or it has flaked partly or wholly on different parts of the squares.A cross-cut area significantly greater than 15%, but not significantlygreater than 35%, is affected. 4 Flaked along the edges of the cuts inlarge ribbons, and/or some of the squares has detached partly or wholly.A cross-cut area significantly greater than 35%, but not significantlygreater than 65%, is affected. 5 Any degree of flaking that cannot evenbe classified by classification 411. Bleeding

The colour bleeding of inks occurs due to the water vapour producedduring the DPL process, which deplaces colour pigments or dyes. Anevaluation was made in accordance with a criterion described in Table 2.

TABLE 2 Criterion Observation 0 no bleeding 1 some bleeding visible bymicroscope 2 some bleeding visible by the naked eye 3 large amount ofbleeding visible by the naked eye12. Blisters

The further crosslinking of the melamine-formaldehyde resin during theDPL process forms water which due to the high temperature is immediatelyvaporized and may cause delamination between e.g. the decorative layerand the protective layer resulting in an enclosed raised spot (as inpaint) resembling a blister.

TABLE 3 Criterion Observation 0 No blisters 1 some small blisters 2large blisters 3 delamination of protective layer

Example 1

This example illustrates an aqueous inkjet ink set which is suitable forprinting colour patterns for flooring laminates and which also hassufficient reliability for industrial inkjet ink printing.

Preparation of Inkjet Inks

Each of the inkjet inks was prepared in the same manner by diluting aconcentrated pigment dispersion with the other ink ingredients.

The concentrated aqueous pigment dispersion was made in the same mannerfor each colour pigment by mixing a composition according to Table 4 for30 minutes using a Disperlux™ Yellow mixer.

TABLE 4 Component Concentration (wt %) Pigment 15.00 Edaplan 15.00Proxel 0.02 Water to complete 100.00 wt %

Each concentrated aqueous pigment dispersion was then milled using aDynomill™ KDL with 0.04 mm yttrium stabilized zirconium beads YTZ™Grinding Media (available from TOSOH Corp.). The mill was filled to halfits volume with the grinding beads and the dispersion was milled for 3hours at flow rate of 200 mL/min and a rotation speed of 15 m/s. Aftermilling, the dispersion is separated from the beads. The concentratedaqueous pigment dispersion served as the basis for the preparation ofthe inkjet ink.

The inkjet inks were prepared by mixing the components according to thegeneral formulation of Table 5 expressed in weight % based on the totalweight of the ink. The component TEA was used to obtain a pH between 8.5and 8.2. Water was added to complete the ink to the desired pigmentconcentration.

TABLE 5 Component (in wt %) C R Y K PB15:3 2.20 — — — PR254 — 2.70 — —PY151 — — 3.85 — PBL7 — — — 2.70 Edaplan 2.20 2.70 3.85 2.701,2-Hexanediol 3.00 3.00 2.50 3.00 Glycerine 20.00 20.00 20.00 20.00 PEG200 20.00 18.00 13.00 — PEG 600 — — — 11.90 Proxel 0.01 0.01 0.01 0.01TEA 0.60 0.50 0.70 0.50 Water to complete 100.00 wt % Viscosity (mPa ·s) at 32° C. 5.5 5.3 4.6 5.2 Surface Tension (mN/m) 35.9 35.6 35.4 35.6Average particle size (nm) 153 150 220 123

The yellow inkjet ink was found to be the most critical one forperformance of the four inkjet inks. As reliability for industrialinkjet printing becomes more critical at higher pigment concentrations,a number of yellow inkjet inks Y1 to Y10 were prepared in the samemanner as the inkjet ink Y of Table 5, except that the concentration ofthe yellow pigment and the dispersant was increased to 4.70 wt % basedon the total weight of the yellow inkjet ink.

TABLE 6 Inkjet Ink Type of Pigment Y1 PY151 Y2 PY74 Y3 PY110 Y4 PY128 Y5PY120 Y6 PY73 Y7 PY154 Y8 PY55 Y9 PY97 Y10 PY138Evaluation and ResultsLatency

The latency of the cyan, magenta, black inkjet inks of Table 7 and theyellow inkjet inks of Table 8 having a pigment concentration of 4.70 wt% was tested. The results are shown by Table 7.

TABLE 7 Inkjet Ink Type of Pigment Latency C PB15:3 More than 30 minutesR PR254 More than 60 minutes K PBL7 More than 30 minutes Y1 PY151 Morethan 30 minutes Y2 PY74 More than 30 minutes Y3 PY110 Less than 10minutes Y4 PY128 Less than 10 minutes Y5 PY120 More than 30 minutes Y6PY73 Less than 10 minutes Y7 PY154 Less than 10 minutes Y8 PY55 Lessthan 10 minutes Y9 PY97 Less than 10 minutes Y10 PY138 Less than 10minutes

From Table 7, the latency of the cyan, magenta, black inkjet inksexhibited good latency, while only the yellow inks containing thepigments PY151, PY74 and PY120 exhibited good latency.

Ink Stability

The ink stability was tested by comparing the average particle size andthe viscosity after a heat treatment of 1 week at 60° C. The results areshown in Table 8.

TABLE 8 Average Particle Size Viscosity % Increase % Increase after 1week after 1 week Inkjet Ink Pigment nm at 60° C. mPa · s at 60° C. CPB15:3 153 0% 5.5 0% R PR254 150 1% 5.3 0% K PBL7 123 0% 5.2 0% Y1 PY151220 0% 4.6 0% Y2 PY74 140 16%  4.7 5% Y3 PY110 166 0% 4.2 4% Y4 PY128188 114%  6.5 190%  Y5 PY120 189 0% 4.2 0% Y6 PY73 250 0% 5.0 0% Y7PY154 266 81%  4.3 13%  Y8 PY55 175 0% 4.4 0% Y9 PY97 224 3% 5.0 0% Y10PY138 174 0% 5.4 0%

It can be seen from Table 10 that the inkjet inks containing the yellowpigments PY128 and PY154 exhibited insufficient ink stability forreliable printing in an industrial environment.

Lightfastness

A colour patch of 100% surface coverage was printed using a KJ4B Kyoceraprint head at a head temperature of 32° C. at 600 dpi on a MH papersubstrate.

The lightfastness of the yellow inkjet ink was again found to be themost critical one. The lightfastness results of the printed samplesbefore and after 1 week of Xenon exposure are shown in Table 9,respectively Table 10.

TABLE 9 Inkjet Ink Pigment L* a* b* C* H* Y1 PY151 89.12 −14.98 91.2392.45 99.32 Y2 PY74 85.56 −6.81 107.70 107.91 93.62 Y3 PY110 78.26 13.99111.79 112.66 82.87 Y4 PY128 89.22 −19.72 94.72 96.75 101.76 Y5 PY12086.20 −12.31 91.55 92.38 97.66 Y6 PY73 86.77 −10.92 102.94 103.51 96.06Y7 PY154 88.36 −11.99 91.43 92.21 97.47 Y8 PY55 82.31 4.18 120.76 120.8488.02 Y9 PY97 88.25 −13.40 97.61 98.53 97.81 Y10 PY138 88.69 −20.8592.91 95.22 102.65

TABLE 10 Inkjet Ink Pigment ΔL* Δa* Δb* ΔC* ΔH* ΔE94* Y1 PY151 0.19−0.95 −1.73 −1.56 1.21 0.61 Y2 PY74 −0.53 0.29 −0.10 −0.12 0.28 0.54 Y3PY110 0.51 −2.04 0.34 0.07 2.07 0.92 Y4 PY128 0.08 −1.40 −2.34 −2.031.82 0.83 Y5 PY120 0.84 −1.36 −1.33 −1.14 1.52 1.07 Y6 PY73 −1.72 0.080.02 0.00 0.08 1.72 Y7 PY154 0.02 −0.80 −1.28 −1.17 0.95 0.46 Y8 PY553.13 −8.59 12.31 11.64 9.48 5.16 Y9 PY97 −0.06 −1.44 −0.85 −0.65 1.540.63 Y10 PY138 −0.49 −2.45 −4.32 −3.73 3.28 1.57

The best results for Xenon lightfastness were found for the yellowpigments PY151, PY74, PY154 and PY97.

Since the inkjet inks containing PY154 and PY97 failed on reliableinkjet printing and the other yellow inkjet inks performed poorly in theXenon lightfastness test, only the yellow inkjet inks Y1 and Y2containing PY151, respectively PY74 were submitted to the Blue WoolScale test. Table 13 gives the lightfastness results of the yellowinkjet inks Y1 and Y2 by using the Blue Wool Scale test.

TABLE 11 Inkjet Ink Pigment Blue Wool Scale Y1 PY151 6 to 7 Y2 PY74 <3

Although the ink Y2 scored a bit better than the ink Y1 on the Xenonlightfastness test, the ink Y2 surprisingly failed on the Blue WoolScale test using sun light. The yellow inkjet ink Y1 met theexpectations of the flooring industry with a rating on the blue woolscale of more than 6.

Metamerism

The metamerism was evaluated using as reference material, a coating of aUV curable yellow inkjet ink Agora™ G2 from Agfa Graphics nv. Such anink is successfully used for printing on plastic surfaces, for exampleon furniture side bands of a laminate MDF panel.

The Agora™ G2 inkjet ink was coated at a thickness of 6 μm on a PET100substrate using a bar coater. The coated sample was fully cured using aFusion DRSE-120 conveyer, equipped with a Fusion VPS/1600 lamp (D-bulb),which transported the sample under the UV-lamp on a conveyer belt at aspeed of 20 m/min.

As second material for the metamerism test, a sample was printed ofyellow inkjet ink using a KJ4B Kyocera print head at a head temperatureof 32° C. at 600 dpi on a paper substrate PGA at 100% surface coverage.The results of the metamerism are shown in Table 12.

TABLE 12 Inkjet Ink Pigment MI Y1 PY151 0.99 Y2 PY74 3.67 Y3 PY110 9.77Y4 PY128 0.63 Y5 PY120 2.36 Y6 PY73 2.01 Y7 PY154 1.90 Y8 PY55 1.93 Y9PY97 2.31 Y10 PY138 0.40

Table 14 shows that only the reliable, lightfast inkjet ink Y1 has ametameric index value of no more than 1.00.

Example 2

This example illustrates the manufacturing of a decorative surface usinga manufacturing method.

Manufacturing of Decorative Surface

An 80 g/m² porous paper used for decor printing was impregnated with anaqueous solution containing 60 wt % of melamine-formaldehyde based resinand dried before inkjet printing to a residual humidity of about 8 g/m².

A decorative layer was obtained by printing a decorative pattern on themelamine-formaldehyde based resin impregnated paper using ink from theCRYK inkjet ink set in Table 7 and a KJ4B Kyocera print head at a headtemperature of 32° C. at 600 dpi. The dry weight of the jetted ink wasless than 1 g/m².

An assembly was made as shown in FIG. 3, wherein the prepared decorativelayer was interposed between a HDF core and protective layer ofunprinted melamine-formaldehyde resin impregnated paper containingaluminium oxide for durability. The assembly was then heat pressed intoa laminate by a DPL process using 138 bar and 50 kg/cm². Twocombinations of temperature and time A and B as shown in Table 15 wereused for melting the thermosetting resin and melding the layerstogether.

TABLE 13 T/t -Condition Temperature T Time t A 140° C. 90 sec B 195° C.[0020] cEvaluation and Results

The resulting floor laminates were examined for adhesion, bleeding andblister formation. The results are given in Table 15.

TABLE 14 T/t -Condition Adhesion Bleeding Blisters A 1 3 0 B 1 2 0

The floor laminates exhibited good adhesion and no blisters, while theamount of bleeding decreased with increasing temperature and time andthe image quality was found sufficient for low-end laminate flooring.

The image quality and bleeding of the decorative pattern on themelamine-formaldehyde based resin impregnated paper was compared withthe same decorative pattern printed on a non-impregnated paper. Thecolour pattern on a paper not impregnated by the melamine-formaldehydebased resin exhibited unacceptable image quality, due to low opticaldensity and excessive bleeding. It was found that the application of atypical inkjet receiver coating on the paper not impregnated bymelamine-formaldehyde based resin improved the image quality, butresulted also in an inhomogeneous and slower thermosetting resin pick-upafterwards leading to inferior adhesion.

Example 3

This example illustrates the advantageous effects on image quality bythe addition of a polymer latex binder to the aqueous inkjet inks, asrequired by the present invention, while maintaining good results onadhesion and blister formation.

Preparation of Inkjet Inks

A first aqueous inkjet ink set S1 was prepared by using the sameconcentrated pigment dispersions of Example 1 and mixing the componentsaccording to Table 16.

TABLE 15 Component (in wt %) in S1 C R Y K PB15:3-concentrateddispersion 20.0 — — — PR254-concentrated dispersion — 20.0 — —PY151-concentrated dispersion — — 20.0 — PBL7-concentrated dispersion —— — 20.0 Capstone ™ FS3100  0.7  0.7  0.7  0.7 Emuldur ™ 381A 30.0 30.030.0 30.0 Water 29.3 29.3 29.3 29.3 2-Pyrrolidone 20.0 20.0 20.0 20.0Viscosity (mPa · s) at 32° C.  3.4  3.9  4.3  5.3 Surface Tension (mN/m)20.7 20.3 19.5 19.3

A second aqueous inkjet ink set S2 was prepared by mixing the componentsaccording to Table 17.

TABLE 16 Component (in wt %) in S2 C R Y K Cab-O-jet ™ 450C 20.0 — — —Cab-O-jet ™ 465M — 20.0 — — Cab-O-jet ™ 470Y — — 20.0 — Cab-O-jet ™ 300— — — 20.0 Capstone ™ FS3100  0.7  0.7  0.7  0.7 Emuldur ™ 381A 30.030.0 30.0 30.0 Water 29.3 29.3 29.3 29.3 2-Pyrrolidone 20.0 20.0 20.020.0 Viscosity (mPa · s) at 32° C.  2.9  3.1  3.0  3.4 Surface Tension(mN/m) 19.0 19.3 18.7 19.1

A third aqueous inkjet ink set S3 was prepared by mixing the componentsaccording to Table 18.

TABLE 17 Component (in wt %) in S3 C R Y K D75C (C.I. Pigment Blue 15:3)20.0 — — — D71M (C.I. Pigment Red 122) — 20.0 — — D75Y (C.I. PigmentYellow 74) — — 20.0 — D73K (Carbon Black) — — — 20.0 Capstone ™ FS3100 0.7  0.7  0.7  0.7 Emuldur ™ 381A 30.0 30.0 30.0 30.0 Water 29.3 29.329.3 29.3 2-Pyrrolidone 20.0 20.0 20.0 20.0 Viscosity (mPa · s) at 32°C.  3.3  4.9  3.4  4.5 Surface Tension (mN/m) 20.2 19.6 19.1 20.5

The same method for making a decorative surface as described above inExample 2 was used, except that the assembly according to FIG. 3 was nowheat pressed into a laminate by a DPL process using 138 bar and 50kg/cm² for 30 seconds at 180° C. A colour pattern of each individualinkjet ink was printed and evaluated.

Evaluation and Results

The resulting floor laminates evaluated for adhesion, bleeding andblister formation are given in Table 19.

TABLE 18 Ink set Inkjet ink Adhesion Bleeding Blisters S1 C 1 2 0 R 1 10 Y 1 1 0 K 1 1 0 S2 C 1 1 0 R 1 0 0 Y 1 0 0 K 1 1 0 S3 C 1 2 0 R 1 0 0Y 1 2 0 K 1 0 0

The image quality was much better than in Example 2. No or minorbleeding was observed due to the inclusion of a latex in the inkjet ink.The inclusion of a latex can be seen as an in-situ formed ink-receivinglayer, but not exhibiting barrier-layer properties.

REFERENCE SIGNS LIST

TABLE 19 11 Paper manufacturer 12 Paper roll 13 Decor printer 14 Gravureprinting 15 Inkjet printing 16 Decor Paper roll 17 Warehouse 18Impregnation 19 Cutting to size 20 Floor laminate manufacturer 21 Floorlaminate 30 Decorative panel 31 Core layer 32 Groove 33 Tongue 34Decorative layer 35 Protective layer 36 Balancing layer 37 Relief

The invention claimed is:
 1. A method for manufacturing decorativesurfaces, the method comprising the steps of: impregnating a papersubstrate with a thermosetting resin; inkjet printing a color patternwith one or more aqueous inkjet inks containing a polyurethane basedlatex binder on the thermosetting resin impregnated paper substrate todefine a decorative layer (34); and heat pressing the decorative layer(34) between: a) a core layer (31) and b) a protective layer (35)including a second thermosetting resin impregnated paper into adecorative surface; wherein the color pattern contacts the protectivelayer (35); the thermosetting resin of the decorative layer (34) and thethermosetting resin of the protective layer (35) is a melamine basedresin; the color pattern includes less than 6 g/m² ink dry weight; andthe one or more aqueous inkjet inks define an aqueous inkjet ink setconsisting of a cyan aqueous inkjet ink, a red aqueous inkjet ink, ayellow aqueous inkjet ink, and a black aqueous inkjet ink, wherein thered aqueous inkjet ink includes a color pigment selected from the groupconsisting of C.I. Pigment Red 254 and mixed crystals thereof.
 2. Themethod according to claim 1, wherein the protective layer includesparticles in an amount between 1 g/m² and 100 g/m², and the particlesare ceramic particles or mineral particles selected from the groupconsisting of aluminum oxide, silicon carbide, silicon oxide, siliconnitride, tungsten carbide, boron carbide, and titanium dioxide, or anyother metal oxide, metal carbide, metal nitride, or metal carbonitride.3. The method according to claim 1, wherein the protective layer isembossed with a relief corresponding to the color pattern.
 4. The methodaccording to claim 1, wherein the thermosetting resin impregnated papersubstrate of the decorative layer is colored.
 5. The method according toclaim 1, wherein the yellow aqueous inkjet ink includes a color pigmentselected from the group consisting of C.I. Pigment Yellow 151, C.I.Pigment Yellow 74, and mixed crystals thereof.
 6. The method accordingto claim 1, wherein the cyan aqueous inkjet ink includes a copperphthalocyanine pigment; the yellow aqueous inkjet ink includes a colorpigment selected from the group consisting of C.I. Pigment Yellow 151,C.I. Pigment Yellow 74, and mixed crystals thereof; and the blackaqueous inkjet ink includes a carbon black pigment.
 7. A decorativepanel obtained by the method according to claim 1, wherein thedecorative panel is selected from the group consisting of flooring,kitchen, furniture, and wall panels.
 8. The decorative panel accordingto claim 7, wherein the decorative panel includes a tongue and a groovemechanical joint that requires no glue.